Translation of electromagnetic waves



Nov. 17, 1953 c. c. CUTLER 2,659,817

TRANSLATION OF ELECTROMAGNETIC WAVES Filed Dec. 31, 1948 9 Sheets-Sheet 1 Ha. FIG. IA FIG, 1B

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0 4 MPH IUDE' Z LEM MODE LEM MODE INVENTOR C. C. GUTL ER AGENT Nov. 17, 1953 c. c. CUTLER 2,659,817

TRANSLATION OF ELECTROMAGNETIC WAVES Filed Dec. 51, 1948 V l 9 Sheets-Sheet 4 FIG. 20

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HORN H ("Fl- TRANSCEIVER A p -g w 231' 239 TRANSCEIVER B INVENTOR C. C. CU TL E R AGENT Nov. 17, 1953 c. c. CUTLER 817 TRANSLATION OF ELECTROMAGNETIC WAVES Filed Dec. 31, 1948 9 Sheets-Sheet 5 F/G. 25 M Hm 25s 258 TM 259 254 nnnnfinrlnnnnnnfinnn 255 l 25/ v I2 Ll UUUU UU ULIU 252 I; TRANSCEIVER B -TRANSCEIVER A IN l/E N 7' OR c. c. CUTLER NOV. 17, 1953 c, c, g T 2,659,817

' TRANSLATION OF ELECTROMAGNETIC WAVES Filed Dec. 31, 1948 9 Sheets-Sheet 6 I FLEx/BLE 352 15/ 345 5/ SECTION 355 I A TM r r 1 FIG. 3 HORN v 36/ TMNsCE/VERA I I I a I fumes/ER a Q w I I a J62 J63 INVENT R c ER By Nov. 17, 1953 c, c. CUTLER 2,659,817

TRANSLATION OF ELECTROMAGNETIC WAVES Filed Dec. 31, 1948 V 9 SheetsSheet' 7 FIG. .38

FIG. 4/ I l DELAY OR PHASE SHIFT lul nulunlnnlm-l /N [/5 N TOR c. c. cu 7L ER AGENT Nov. 17, 1953 c. C. CUTLER ,659,817

TRANSLATION OF ELECTROMAGNETIC WAVES Filed Dec. 31, 1948 9 Sheets-Sheet a FIG. 45 456 FIG. 46

SIGNAL 7 TRAA/scnvm PARALLEL POLARIZATION.

FIG. 49 PERPEND/CULAR POLARIZATION Tl-IE' new Rom rss 41' RA r: w

INVENTOR C. C. CUTLER MB W AGENT NOV. 17, c, C CUTLERv 2,659,817

TRANSLATION OF ELECTROMAGNETIC WAVE Filed Dc. 51, 1948 9 Sheets-Sheet 9 t i 1 f m a: w 7 Elk u INVENTOR C. C. CUTLER AGENT Patented Nov. 17, 1953 UNITED STATE ATEN'I' OFFICE Cassius C. Cutler, Gillette, N. .L, assignor: toBell Telephone Laboratories, Incorporated, New York, Y.,, a corporation of New York Application December 31, 1948, serial No. 68.549-

6 Claims.

This invention relates to electromagneticwave guides and wave guide systems.

object of the invention is to control the propagational characteristics of electromagnetic wavesb'y guiding them along? a conductive surface, provided with regularly spaced. discontinuities such as corrugations, grooves, slots or projection thereon.-

Further objects of the invention are electromagnetic transmission and reception, wave delay and. phase control, frequency filtering, mode conversion, mode discrimination and suppression, radiation and. radiation pattern control, and control ot the interaction between electronic streams and electromagnetic waves.

in accordance with vario,usemhodirnents of the invention, metal ic surfaces are corrugated, in order to provide new types of electromagnetic propagation in a direction perpendicular to the guiding corrugations; These types difier from electromagnetic waves in free space, or near smooth conducting surfaces, in that their energy is contained in a region very close to the surface, with the field strength decreasing exponentially away from it. Wave energy follows such corrugated surfaces closely, even it they are bent or warped. The elctromagnetic waves: in this case are trulvguide'd waves even though not necessarily fully confined within physical boundaries. Also, such waves may have a longitudinal component of electromagnetic field in the direction of propagation, similar to that of'the more conventional waves, propagating ever known forms of wave: guides; However, they differ essentially from the conventional: guided waves in that the velocity and impedance associated therewith, depend: on the corrugated contour of the guiding surface; the velocity-being in general slower than that in free space. I

accordance with some embodiments of the invention, two general conductive surface con,- d-itions are disclosednamely, (.1) where the slots 01:; corrugations are less than one-quarter wavelength deep and (2.), where they arebetween onequarter and one/nan wavelength deep whene n is. an integer 0, 1,3, etc. and N is the free space wavelength.

Irrthe first" case, which: may be terms-diam in-- ductivef surface, the lowest order modeis propagated with velocities ranging from zero to infinity; depending on how the wave is confined The external waves exist and are propagated at a velocity slower than infree space. In the second case, which might be called a capacitive sur face, the wave's'are not guided unless fully con fined, whereupon they will propagate with velocities greater than that of free space: and with properties'similar to conventional guided waves. In both cases, the higher order modes are always transmitted with velocities greater than that: of free space or of the dielectric medium or filling associated with the corrugated conductor systems.

In this specification, the modeor transverse magnetic mode is characterized by having no longitudinal component of magnetic-force; whereas the longitudinal electromagnetic mode has longitudinal electric and magnetic field components and may also bereferred to as hybrid waves as S. A.- Schelkunofis book Electro- Magnetic waves,"- puhlished in 1 943- in New York by Van No'strand Company.

Referring tothe figures of the draur-ing:

Fig. l. showsa corrugated planar surface for guiding electromagnetic waves;

Figs. 1A and 1B are explanatory diagrams associated; with Fig. 1;; v

Fig. 2. shows a corrugated solid rod for guiding TM or transverse magnetic mode electromagnetic waves;

Figs. mans 2B are associated explanatory dia grams;

Fig. 3 shows a corrugated solid rod for guiding LEM or longitudinal electromagnetic mode waves;

Figs. 3A and 3B show explanatory diagrams;

Figs. 4 and 5 show regularly spaced conductive discs for propagating LEM and TM modes, respectively;

Figs. 6 to. 9 inclusive show spaced corrugated conductive sheets for guiding. waves" of TM mode? Figs. 10; 16A, 11 and 11A show hollow rectangu- Tar wave guides with internal corrugations;

Figs. 1033, 100", 1113; no show explanatorydi'a grams;

Figs. 12,13. and 14show hollow cylindrical: wave guides. with iuternar corrugations;

Figs. 12A, 12B, 13A, 1313, 14A, 1413' show explanatory diagrams;

Figs. 15, 16, 17 show v'arious illustrative modifications ot fabricated corrugated surfaces;

Fig. 18 shows a trough-shaped corrugated surface;

Figs. 19, 20, 21, 23, show various modifica" tions of radio transmission and reception systems involving corrugated surfaces;

Fig. 22 shows a corrugated surface lens for radio use;

Fig. 24 shows a modified rectangular corrugated wave guide;

Figs. 26, 2'7 show wave guide radiating structures for converting from interior to exterior wave propagation along corrugated surfaces;

Figs. 28, 29 show coaxial cables having inner corrugated conductors;

Fig. 30 shows similar mode converters involving corrugated guides utilized in a communication system;

Fig. 31 shows corrugated wave guides for providing a transition between interior and exterior wave propagation;

Figs. 32, 33 are cross sections of the transition showing exit slots for TM and LEM mode propagation respectively;

Figs. 34, 35 show a transmission signaling system utilizing propagation over the interior and exterior of hollow corrugated pipes;

Fig. 36 is a modification of the signaling system shown in Fig. 23;

Figs. 37, 38, 41 show variants of corrugated wave guides;

Figs. 39, show corrugated guide phase shifters;

Fig. 42 shows a corrugated guide mode converter;

Fig. 43 shows a corrugated guide filter;

Fig. 44 shows a standing wave detector;

Fig. 45 shows a corrugated guide wavemeter;

Fig. 46 shows a reflecting piston on a corrugated rod;

Figs. 47, 50 show signalling systems;

Figs. 48, 49 and 49A illustrate antenna arrays involving corrugated wave guide structure;

Figs. 51A, 51B, 51C show electron tubes involving corrugated wave guide construction.

I. Single corrugated planar surface Referring to Fig. 1 of the drawing, l represents an extended conductive surface which may be planar as shown or curved, and has thereon a series of transverse rectangular corrugations 2, uniformly spaced and separated by notches or slots 3. The slot width a is generally a small fraction of a wavelength, for example,

the corrugated surface may be termed inducfi because the input impedance across each while the ratio slot is inductive and the storage of field is predominantly magnetic. A traveling surface wave exists, which propagates along the direction Z and is guided by the corrugated surface I with a velocity 2;, dependent on Z, the corrugation depth, and varying from free-space velocity at zero depth, to zero velocity at one-quarter wavelength depth. The impedance (E/H) of the wave varies inversely from free-space impedance characterized by a smooth surface and 1:0, to infinite impedance for a quarter-wave depth of corrugation 2. The variation of field strength away from the corrugated surface I changes from a very slow exponential decrease with a shallow slot to a very fast exponential decrease as the slot depth approaches one-quarter wavelength.

The lines of force for a transverse magnetic TM wave are shown in Fig. lAthe solid lines representing electric force E and the dotted lines perpendicular thereto, the magnetic force H.

Fig. 1B shows the amplitude of the field components as a function of the perpendicular distance above the corrugated planar surface I.

There is a longitudinal component E2 of the electric field in the direction of propagation Z. After a certain distance all components of the electromagnetic field EX, Ey, Ez diminish rapidly with distance from the corrugated surface so that the flow of energy is effectively confined to the immediate vicinity of the corrugated guiding surface 2. It is found that the waves still adhere to the surface even when it is curved or warped. The phase velocity and wavelength are less than those of a wave of the same frequency guided by a smooth planar conductive surface. The corrugated surface also has inductive characteristics when or more generally when When the depth of the corrugation Z the corrugated surface is designated as a capacitive surface. Here the variation of field with distance from the corrugated surface changes from the large negative exponential characteristic l of the inductive surface to the large positive exponential Z. In this case, the field increases indefinitely away from the surface. so that the wave is no longer guided. Instead, a plane wave near the surface tends to be slowed, and will be transmitted parallel to the surface with a field decreasing toward the surface, the rate of decrease being greater, the nearer the corrugations are to one-quarter wavelength in depth. In other words, the surface is unable to guide a wave and the flow of power is directed into the space above the corrugation instead of being confined to the vicinity of the surface. When the oscillations in adjacent slots are in opposite phase and a complete standing wave will exist on the corrugated surface. The wavelength of this standing wave is twice the distance between the mid-portions of adjacent slots 3, 3.

II. Single corrugated rod Fig. 2 shows a long corrugated circular rod 2| propagating a transverse magnetic mode TM.

a hast;

F s 2 show the e ectr c E). aha; haeceth.

(H l lines of force for a tran sye e ma MQQIQ here E 1. 959 19 the qoh ueated root hs qw rt the ee ax As is apparent by comparison of the field.

Q... h; the. ttahhmiss ch.

ass

eqhshts. as. uhqtich oi a, he. 1...d.ia i %....Q.Q L

iremthe r 51 male, 3 3 or. i a hmhhr ies t he. hie-d sho n v. I

b hhhises h s ie efhhraheh. re ular y eras d q hqh ht v i 2' he ha .hhhh h immersed in a dielectric medi m. be. d: Q e -1. A ernative h 159 5. may he fled apar d l ctric sh Q r hihehi. he discs l-l'is ofthe order of 1%; Wavelen p nama;- thih h h x aqti h 0? he i -heme F 1.. illustra e he hhhesethh o an LEM m d thi i hsh h he as h i ated', whereas Fig. 5 depictsithe propagation 01f positely directed current existsbetvveen adiaeeiit plates 42, 42'. The diameter of the discmay be in the aheetrmih QS' Za.

With respect to the electromagnetic properties or the discline M showr i n Fig. 5 the propagation chi-{M modes thereon; corresponds to the hr hhsat Q 1t hh esh -me.hh "he ha all h htearr h ehh h ih. the?" res nant he rhh xhesihh h ahhsas. .c ihrphrtihfleth were. is;

aerate 13.. 2;: Ihaeleqtr e c r ent distri u n b w .11 t 2 ht d by the h rt 74!?! urren dist ics1 lar to those of; Fig. 2, y oi structures is made even m the dot-dash representation Q2 o 111. .11 1 N91 5. Pas h h or ad ,t i S11 i i..i.i 5-. he. discs ahh hyhe h t or of eh III. Parallel corrugated sheets h? to 3 iml fiil fi two. ha paral l.

corrugated plates or sheets 6!, 61" with their respective corrugations 62, 62' facing each other l he. corrugations are. structurally like those (QI; Fig. 1-. Thereare twopossible modes of prophgation for shallow corrugations, both being,

the hrsttr hst hsh mash t h TM .(l i

hh h hihh p opa a p r endicular to slot d ection, at SlOWQ I hit er-$3 95? dhelhy- F 6; thematic whe eas; Eta: 7

Thus, the TM rnqde shown in Fig. (5 travelsmpre slowly asthespaea me 4d eats sma le Wh e h im e ance (El i rises indefinitely. There is no cut-off spacing 2.5- heqhehcy for this m de, and, its is-suhh ha it ma also e r pa a ed hetweeh single eri-heated. lateahd a m oth zehe ehhe: P ate, W th. alf the. P at sep ration "if-he econ PM ode t e 8 mhas t s th. sine th. smaller ac and. hu f spa n 2.4 and. a qwer dehehdlhe when h pth. of his a e e ery er s a lana .1 component at elec ri fie d, it can only ph..-.ae he-betwhhh t Q o g ed plates.

h r. th s ot depth greater ha one.-

w elhhgth both M mod s (Fish a d:

.hm .tt wi h tewhi es lwa s r ate than the velocity in free space. The velocity dependsupon theslot depth land the spacing 203, being greater for smaller spacings. With a given depth. ll. he ches w below h c @dhl lagoon-$1 s h Qnahalf wavele he. dep a p a hes 7 th I is smaller than one-.. h, h eheh M r-m d m ter-1 yw tohoselesc hed n the preceding paragraph. As the slot is deepened, the cut-off separation 913 these modes becomes smaller till the depth reaches one-quarter wavelength and the first modes disappear. At this point the higher order modes become dominant and vary continuously identical to the previous next lower order modes but with one-half waveehethq eher hhr uga i w l t nd; fi b da c itih thevariatihh o e c y w h e yis hat the W"'m O (1-3 varies; from a finite ofrfree space depending rlih e hs h e am oh 01: a. at. v ry; req e s o ze v lo y higher freque cy cu -o f," here th slot The diameter oflim hi s sp in depth is a quarter wavelength. This has the characteristics, therefore, of a low-pass filter. As the frequency is continuously increased, transmission takes place again, at very high velocities, decreasing to the free-space velocity for the frequency where the slot depth is one-half Wavelength, and then decreasing to zero and another cut-ofi, at the frequency for which the slot depth is threequarters of a wavelength. In this region it has the characteristics of a band-pass filter.

The second LEM mode varies similarly with frequency, except that it has a definite low frequency cut-off.

IV. Transmission within rectangular guide, with corrugated upper and lower walls. Longitudinal electromagnetic waves Figs. 10, 11, A and 11A show a corrugated rectangular guide IOI whose upper and lower walls a are provided with corrugations I02, and whose side walls I) are smooth. Their propagational characteristics for the first and second LEM modes (Figs. 11 and 10) are similar to the case of the parallel sheets, except that there is superimposed on the latters effects above de-' scribed, an additional low frequency cut-off limitation, and a speedingup factor due to the width a. For rectangular corrugated guides whose widths a are reasonably greater than a half wavelength, the characteristics are nearly the same as for the corrugated sheets, illustrated in Figs. 8 and 9. Figs. 10B, 10C, 11B, 11C show the amplitude characteristics of the field components.

By letting the height I) of the rectangular guide become very large, the fields become approximately exponential functions of the distance from top to bottom surfaces I02 which means that for shallow slots the waves are confined near the corrugated surfaces I02. Also, such waves can likewise be guided by a rectangular trough With a corrugated bottom. The side walls of such a trough need not be perpendicular to the bottom, but may be at any angle, or even completely removed leaving a corrugated sheet of limited width. The velocity is different, but propagation is still possible under these conditions. Figs. 10A, 10B and 100 show the field distributions and the amplitude of the field components.

V. Transmission inside a corrugated circular cylinder transverse magnetic mode Fig. 12 shows a corrugated hollow circular cylinder I2I propagating a transverse magnetic mode TM along the interior thereof. The corrugations I 22 are uniform circular rings concentric with the cylinder wall I2I. They may be integral therewith, welded thereto or formed therein in any desired manner. The slot depth whereas in Fig. 13

l 1 X i For propagation through the interior of cylinders I2I, Figs. 12 and 13, the velocity and impedance for the TM circularly symmetrical mode are dependent upon the diameter d of the cylinder, as well as the slot depth 1 and all waves have a definite low frequency cut-off. When the slot depth l is less than a quarter wavelength, the velocity will vary from infinity at the cutoff diameter d to a finite value slower than free-space velocity for very large diameters. Both the cut-off diameter for a given frequency, and the asymptotical velocity for large diameters is determined by the depth 1 of the slots I23 in terms of wavelength.

Figs. 12A and 123 show the field distributions and Figs. 13A and 133 show the field components variation with distance corresponding to the mode propagations illustrated in Figs. 12 and 13.

For slot depths between one-quarter and onehalf wavelength, the velocity as a function of diameter is very similar to that for smooth circular wave guide, except that the cut-01f diameter d may have any value between that for the lowest circular electric mode in a circular pipe, and the lowest transverse magnetic mode in such pipe, depending upon the depth of slot. In fact for any depth of slot, there is a continuous variation of cut-off diameter, as a function of depth, from zero to any value. As the slot I23 increases in depth, the cut-off diameter for any mode decreases continuously until it reaches zero and disappears.

As a function of increasing frequency, the velocity varies from infinitely fast to zero and, after a, band of no transmission, the velocity repeats the same cycle of variation. For small ratios of diameter to wavelength, there are stop bands between the first adjacent pass bands, but at higher frequencies and for larger diameters where more than one mode of transmission at a time becomes possible, the pass bands overlap.

The longitudinal electromagnetic LEM mode is propagated interiorly through a corrugated circular cylinder as illustrated in Figs. 14, 14A and 14B. Here the velocity and impedance are rather complicated functions of the cylinder diameter near the cut-off, and for large diameters reduce to the general form for other corrugated surfaces.

This mode has a definite low cut-off limit where the cylinder circumference is one wavelength, below which it will not propagate regardless of slot depth. For corrugated hollow cylinders smaller than one wavelength in circumference, the transverse magnetic mode becomes dominant and is the only one that will propagate.

Figs. 15, 16, and 17 disclose various modifications of constructional forms for a corrugated guiding surface.

Fig. 15 shows thin, parallel metal plates I52 embedded in slots in an extended conductive surface I5I. The plates I52 are of uniform height 1 and evenly spaced apart.

Fig. 16 shows a corrugated metal surface formed with sinusoidal undulations IBI uinformly spaced apart thereon, whereas Fig. 17 shows the corrugations as forming resonant cells or cavities I13 of like geometrical dimensions in an extended conductive surface I14.

Fig. 18 shows a trough-shaped conductive surface I8I provided with regularly spaced corrugations I82 and parallel side walls I83. The corrugations I 82 are parallel and extend between the side walls I83.

VI. Signal transmission systems Fig. 19 shows a system for transmitting and receiving electromagnetic waves involving a single corrugated sheet or surface I55 of the type disclosed in Fig. 1. The transceiver I5I is a transmitter or receiver, or a combined transnutter-receiver of the general type known to the art, which is connected to a coaxial line I52.

those inner conductorl fl terihihates 'i1ia prose antenna or radiator I53. The coaxial line I'52 passes through a dielectricrib or corrugation for rigid support and strength. The waves to be transmittedare reflected inproper reenfor'cing phase by parabqlicreflector lfi l and are then propagated along the corrugated surface I55 in the manner described in connection with Fig l. Incoming waves are received and similarly reenf orced by the parabola and antenna I53 to be I directed to the receiver I5I after traversing the coaxial line I52. I 1

,Figs. 20 and 21 are variants of the system of Fig. 19, wherein a probe antenna I63 radiates or receives signals inside a smooth hollow wave guide I64 of circular or rectangular cross section.

A signal generated in transceiver IB'I may be propagated into the" wave guide I6 i, and he then converted without reflection by means of a tapered and corrugated horn I6, 5. The horn I65, as shown in Fig's. 20 and 21, has a tapering smooth surface I661and an Opposed corrugated surface IG'LI 613. Corrugations IG] increase in depth toward the freeend' of horn I65 for matching the impedance of the smooth guide I64 to the impedance of the horn. The corrugations lfifi at the free end of the horn are uniform in depth and evenly spaced.

VII. Corrugated guide Zens Since the velocity of propagation may be con-- trolled bythe' depth'pf slot, a corrugated wave guide lends itselfreadily to the problem of focussing'by radio lenses. Focussing maybe accomplished witha' sipgw corrugated surface wave,

orwith waves between parallel pmesjt introducing a different relative delay forvarious parts of the wave, either by varying the depth, the spacing, or the width of corrugations. An example thereof is showniin Fig. 22.

Fig. 22 disclps s 'a radio lens 221;, wherein the corrugations 222 in the surface vary' in spacing, width and/or'depth to provide the same delay along any path from input 223 to output 224.

The corrugations are made deepin the central region of this structure, and shallow near the edges, as per Fig. 22, so that the surface' vvave having the shortest path from the input to the output travels slowest, and that having the longest distance fastestg The corrugations are ta-' pered in depth between these two situations, and the depth is controlled so that the electrical phase shift is the same along any Wave path. The corrugations 222 are also curved so that they are nearly perpendicular to the directionof wave propagation at any point. This character of the propagating medium is such as to direct, or refract the waves toward the line of lowest velogity. v Therefore the waves initiated at the apex and move in all directions so that at the output the'waves are in phase and directed parallel to the axis. Conversely; a uniphase wave, at the right-hand end of the structure, traveling "to the left, would be focussed to a point at the apex.

Fig.1 23shovvs a two-way transmission system for multiplexedfsig'nals. A common conductive surface 23I is provided with corrugations on 'opposing facs, which may difie'r in spacing and depthyto favor guided transmission of the re's'pectivefrequencies of signals A and B. Signal A is guided along the corrugations of the upper face ifitoandout'ofthe transceiver A The piston P serves to reen-iforc the signal Correspondingly, the signal B is guided along the under f'ace I I 10 a. piston? in ite passage int" "rpm: o'f th transceiver 13, Matching betw' nfthe tapered horn Er, and the smooth wave ides W, .is accomplilh e'd as Fig. 21 {by pr gressively tapering theu deplth of the corrugations on the opposing "faces: of surface 23]. The corrugated free end 2Q!) projects beyond the horn and'ihayloe conted to any tran is's'io'n system capable-of s each as corrugated w e guide system; F

ula'r wave g'uide'fl'l parta u j pf I through. a, holl ow wave guide having ,an external corrugated surface I h e external [surface of the av eu fieis. ine QaX L iQ I For "transmission; transceiver A generates and launches a. signal A qvera coaxial transihis on lin omer gine c dl t r' l'fi 3 3;- T e s na it t fie d if e n e ci 'eg ha 'h iiib f hl pisto .5 T l r} face. o c nd Q r-HI. the coal a1 mode o fl er B generates V r I, tronci aig'netic signals 3 from a probe ant'enn totheh0l10wi nterior of pipe 2 5'I for; conven all Wave. l lide propagation thereth'r'ough, rnepigbezsa which is aneXtension' of the inner conductor of coaxial line 256, liesf alongthei principalijaizis of hollow guide, 25'I.

,Eies; Z61andf21show liad iating structures for transff erring 'an electromagnetic Wave from inside uide' to its ext or'for propagation and a 'cblj'rugated Cand -em integral- W av ';s; transrerred,'rrom a'doir'iinant mode" iii "the rectangular guide I at: through coupling slots to a mode appropriate to the com fte dggui olZEBsituated on the exterior t iiidel 2fil Thi s'pmode has the v'el'o'cltyfasi an fgternal wave je'ajsdrfae 265, fa Itherefore {coupling through slots gfifl.

si oii' or recept interiorlyand exteriorly. v N

For" transmissiorifasource 270' generates a the'j e'x'teriorof the wave guide. a

- wave for.v propagation througha smooth cylindrical pipe 21!. Aconverter section 212 transforms to wave propagation characteristic of hollow corrugated guide 213, which is provided with regular corrugations 211 and a wave barrier 218 at its terminal end. The corrugated guide 2'l3 is provided with external corrugations 215 and coupling slots 214 located on the opposite side from internal corrugations 211. The internal wave propagating through pipe 213 is coupled through slots 214 to the external surface, and is thence guided by exterior corrugations 215 and Fig. '28 shows a coaxial transmission line wherein the inner conductor 28l terminates in .a corrugated rod 284, and the outer conductor 282 is flared outwardly. The corrugated tapering portion 283 near the throat of the flare serves to provide a smooth impedance transition between line sections 28] and 284.

Fig. 29 shows a coaxial line similar in structure to that of Fig. 28, with the flaring horn 285 omitted, and with the inner conductor 29! tapering to a small diameter. The tapering corrugations 293 provide for smooth electrical transition between conductor 29! and corrugated rod 294.

Fig. 30 shows the transition to a LEM mode on a corrugated rod from other types of smooth wave guides and their respective modes, and con- 7 versely.

, A TEu wave in a circular pipe or TEio in rectangular pipe is launched at 305 and transmitted through smooth guide 300 which may be either rectangular or round in cross-section. These modes are transformed into the LEM mode on corrugated rod 309 via a coaxial mode over coaxial line 302, 303. Impedance smoothing transitions are'provided at 302 and 308. The corrugated rod 309 may be used as a transmission system or may be connected to other means of transmission or radiation.

Fig. 31 shows a converter from a coaxial mode of transmission to a mode of transmission characteristic of the corrugated rods disclosed in Fig. 3.

A source of oscillations 3 is connected to coaxial line 3l2, 3I3 whose outer conductor 3l3 has uniformly spaced annular corrugation 3M on its exterior surface. Circumferential slits or openings 3l5, situated between successive corrugations 3M and a reflecting piston 3l6 permit the exit of electromagnetic wave from the interior of the coaxial system to its exterior, where the Waves are converted into a mode characteristic of the corrugated rod, previously disclosed in connection with Fig. 3. The corrugations 3M extending along the outside surface of conductor 3I3 then guide the external waves in the characteristic manner of corrugated rod propagation.

The details of the arrangement of slits 3l5 for TM waves are shown in Fig. 32 while Fig. 33

"shows a different arrangement of slits 335 for providing LEM waves. The location of slits 335 in Fig. 33 is shown as collinear along the direction of the maximum field vector E'; The slits in both figure are out only at points where the relative phases of the waves inside and outside of the guide are the same. In the case of Fig. 32 four slots are cut at each circular section; but in Fig. 33 the alternating slits are at top or bottom of the guide as the case requires, with the axis of the individual slits 335 transverse to the vector E.

Fig. 34 shows a wave-guide transmission syspure TM mode is transmitted. The terminals of ordinary flexible wave guide.

12 tem for modulated waves, wherein a conversion is effected from conventional wave-guide transmission to a form characteristic of corrugated hollow pipes. The source 34L which may be a generator of microwaves such as a reflex klystron, is modulated by speech waves from the microphone 342 to provide modulated waves which are launched by the axial probe antenna 344 into the hollow interior of cylindrical wave guide 345. The antenna 344, which is an extension of the inner conductor 343 of a coaxial transmission line, effectively converts from a coaxial mode of transmission to a. TM wave-guide mode. 'Corrugated hollow pipe wave converter 345, which is integrally or otherwise fixedly interposed in the smooth wave guide 345, provides the transition from conventional TM wave-guide propagation to a TM mode characteristic of hollow corrugated pipe. Other modes such as TE11 which may be excited are reflected at 346 and only the 341 of the corrugated pipe 343 have suitably tapered corrugations to effect a smooth transition whereby freedom from undesired wave reflections is achieved.

Fig. 35 is a prolongation of the system of Fig. 34, with further provision for internal and external propagation of modes characteristic of hollow corrugated pipes. For this purpose, the smooth wave-guide pipe 345 is extended for a suitable distance, and its prolongation 345 in Fig. 35 is then provided with external annular corrugations 3H! and circumferential slits 3l5 as heretofore described for Fig. 31. Thus, in the region of converter section 35l on the left, an internal and external wave of the corrugated pipe type will be established and will propagate to the right of Fig. 35 inside and/or outside of flexible corrugated pipe 355. Reflecting barriers 316 may be used if only external transmission over the flexible section 355 is desired.

At matching section 352, tapered corrugations 353 are provided designed to smoothly match the thin, flexible corrugated wave-guide section 355 to the section 35!. The corrugated wave guide 355 may be a sylphon bellows type with the advantage of having no discontinuities arising from metal-to-metal contacts and the jointing In the transmission line of Fig. 35, the flexible section 355 may be provided with a smaller diameter than normal, without cutting off the normal propagation of desired modes and at the same time suppressing undesired higher order modes.

Transmission on the outside of the flexible section 355 has also the advantage of smaller size, since the external wave is transmitted efficiently when the over-all diameter of section 355 is no greater than one-quarter wavelength. Reception of signaling waves may be accomplished by appropriate changes in the structure of Fig. 35.

Fig. 36 shows a modification of the two-way multiplex communication system disclosed in Fig. 23, wherein the corrugated plate 23! is replaced by a radiator 33!, having a series of parallel equispaced rectangular conductive plates 332 embedded in a dielectric rod 363 of low-loss dielectric material, such as rubber, polystyrene, titanium dioxide, barium titanate or the like. The dielectric material may have a high dielectric constant or it'may have subtsantially the dielectric constant of air, viz., unity. The transceivers A, B and the horn are as described in Fig. 23.

Fig. 37 shows a modified form of wave guide,

"wherein. a series "of" short. length in; several ways.

cylindrical; or. rectangular pipe.

13 parallel equispaced metallic fiat rectangular plates 312 are mounted between fiat metallic longitudinal bars; 351:! to form a ladden-like structure'consisting of similar cells 313.

The cells 313 each comprises a pair of adjacent parallel-plates 3 :12; and the connecting end bar sections 3TH with the intervening dielectric medium, which may be air or any other suitable dielectric fluid or solid, 7 i Fig. 3.8: Shows a wave guide comprising a hollow. cylindrical pipe 3 B! formed of low-loss dielectricmaterial, as described with reference to Fig. 36, in which a seriesof; parallel, equispaced annular conductive plates 382 are embedded. In general, the spacing, thickness and dimensioning of. the plates may be as in Figs. 4 and 5.

The" propagational characteristics of the lpaded wave'guides shown, in Figs. 36 and 38 are dependent on the'ratio of plate spacing to the wavelength in a manner analogous to that dejf nedjfor the. corrugated rod and pipe aforementinned.-

Rhase shifter-and delay transmission line Since the velocity of transmission inyor on guides, with corrugationsless than one-quarter Wavelength deep is slower than in conventional guidesyand maybe-madever slow; such corrugatedaguides. may-be' arranged to give time delaysxor predetermined fixed or variable value.

The corrugated surface may be used as a-phase shiften tolgiveawide; variation of phase in a Firsh the slot depth. in a. corrugated guide maybe varied by pistons, or tuning; screws; to vary the phase velocity. Second; if -a-,sylphon bellows be used to conduct the waves, the-phasemaybe varied by stretching andccmpressing the length of sylphonlbellowsqguide Third, the phase may be variedina, rectangular corrugated guide by varyings-the;height-oi theguide. Since a slow traveling wave may be used, any of the above methods may; be madeto give a greater phase variation in a givenlength, than could be obtained inconventional waveguides;

Fig, 39 shows a conventional wave-guide transmission line with;interposed sections of corrugated wave guide 392 adapted toprovide phase shifts. of predetermined amount in the transmission -.of ;waves I through the long wave-guide pipe;39l'. An advantage-of, the corrugated phase shift section 392 is that short lengths are. adequate to provide appreciablev amounts of delay or phase shift,; which may beeasily varied in, amount-for example, by utilizing an expansible *syl-phon bellows construction as the corrugated guide: 392.; It should, however. be-understood thatlpredetermined or fixed amounts of delay criphase shift are'also'envisaged for the corrugated form of phase shifter.

Fig. 40" disclosesa variable phase shifter utilizing a section of hollow corrugated pipe. A seetion of hollow corrugated pipe 401 is interposed in; a,- smooth wave-guide line 462, for. example, a

face:- 403 Qof t-pipe- 40 l is provided with regularly spaced; corrugations Adieucceeded by shallower corrugations ..4ll5, 4fll which taper in. depth to- Wards; thecnds ofsection 4! for the purpose of impedance matching to the smooth wave guide 402;. Opposite the. corrugated face403, a longitudinal -spring,face-,member 408 is provided, Which' ma-y be.;bowed inwardly or outwardly by handle; 0, 5 to -;vary the cross-sectional dimensions, thereby variably altering the phase ve- One internal 4&5

} ent i. e. greaterthanthewidth of 'thec'orruga- 4 l4. locity of the propagated variable phase shifts.

waves and-- Fig. 41 discloses a corrugated sheet, wherein.

termined by the ganged pistons 4 M,v which are displaceableinto and out of' the chambersby thev movement of the common fast'ening.;plate M5 andhandle M6,.

Fig.42 shows acorrugated type of'modec'onverter for transforming from a dominant 'I'Mbi coaxial mode to a wave-guide TM01 mode. for propagationin smooth. hollow pipe.

The corrugated modev converter section. 421. is connected integrally or by mechanical coupling between a coaxial. line. 422. and a hollow wave-- guide cylinder 423T. .The coaxial' line 4'22 has: connected thereto. generators or transducer structure (not shown) for. propagatingaTMor The converter 425, which supports. aTM mode as heretoforedescribed in connection withFi'gs. 12an'd 1"3',,is: flared out in cross-section -to connect onto Eel-- low cylinder. 423,.which may. be:de'signed to Su'p-- coaxial mode towardthe right.

port a 'INIo1, TM02 mode etc.

The depth of the corrugations lizirmay be uniform alongsection 42l,,until it.appr'oaches pipe 423, whereupon the depth of corrugation may taper as shown .for-accomplishinga'srnooth,

zeglectionless transition in impedance into "pipe Fig. 43 disclosesjafrequency filter; The hollow pipe 431 has a longitudinal corrugated sheet 432 dividing it into two sections. The width of the corrugations 433 on the upper. face'is' differtions 434 on the lower face of 'thcsheet, but the depth of corrugation is otherwise uniform. The length of the sheet'43l'issuch'that'fi passes through the upper and lower sections of pipe in time intervals such .as to appear in the output in phase opposition, whereby, T1 is eliminated but f2 is passedtherebeyond'to a useful load (not shown). The electrical length of the upper and lower 'corrugatedfaces may be represented as L and.

respectively. The corrugated'ends ofthe sheet 432 are tapered for matching impedances.

Figfl4 shows a standing wave detector arrangernent utilizing c'orru'gated wave guide for improved operation. The*pipe"44l has-"conventional rectangular wave=guide end sections *442, andian integral intermediate '.corrugated -waveguide section l ls-ofrectan'gular :type (FigsJlOA and 11A). The regularly spaced-corrugations 444, which merge with-impedance matchingtapered corrugations 445, serve to 1 concentrate the propagated Wave energy passing through/pipe 44! in close proximitythereto-end .-perm-it.:the opening of the top lot-said pipe. |-without ap 'preciable radiation of energy therefromw The inclined flaps 446 in the opening 441 act to match theimpedance of pipe 44! to outside space at the opening, whereas the tapered corrugations 445 match the corrugated section 443 to the end rectangular sections 442. A sliding member 448 bridges the opening 441 and carries the moving retractible probe 443, coaxial conductor, measuring crystal and ammeter arrangement 450.

The reduction of possible radiation from the open top 441 constitutes a desirable improvement over the slotted type of carriage arrangement in the conventional standing wave detectors of the prior art.

Fig. 45 shows a wave meter arrangement suitable for use in connection with corrugated guides and/or smooth wave guides.

A hollow cylindrical wave guide 45!, through which circularly symmetric waves propagate, has attached thereto a wave meter 452, comprising a hollow corrugated pipe 453 with res ularly spaced corrugations 454 therein and a coupling apertured end plate 459. A reflecting piston 455 at the end of pipe 453 opposite to end. plate 459 is associated with a detectin crystal 456, coaxial conductor 451 and ammeter 458 for indicating cavity resonance in the wave meter 452. The piston 455 has quarter wavelength traps 459 in its sides to prevent leakage past it into the space rearward thereof.

The advantages of the wave meter arrangement '(Fig. 45) are to provide a wider band spread for -frequency measurements by the use of smaller diameter and lengths in the wave meter. A large change in piston position corresponds to a small interval of frequencies, thereby providing greater sensitivity and precision in frequency measurement. This improvement is attributable to the decreased velocity of waves in the corrugated hollow pipe 453.

Fig. 46 shows a reflecting piston 46! on a solid corrugated rod 462 having ring corrugations 464. The piston 46! is provided with internal, wave leakage preventive traps 463.

Fig. 4'1 shows a corrugated wave-guide system for transmitting and receiving modulated signal waves.

A signal transceiver 41!, well known in the radar art 2nd microwave radio relay field. is connected to a modulator 412 whose function is to combine the local oscillations from source 413 either with the incoming received signal or with the transmitted signal in a conventional manner.

In. the case of transmission, a modulated microwave is sent over coaxial line 414 for ultimate propagation through a corrugated wave-guide system 415. The terminal probe 416 launches the modulated signal in the form of circular magnetic waves in smooth pipe 418. These waves comprise a TMm mode and others. To obtain a pure 'IMm mode for transmission over the corrugated wave guide 415, a mode filter 411 is connected between the smooth pipes 418, 418'. The mode discriminating filter 411 comprises a section of corrugated pipe of die meter less than approximately .32 wavelength, which is below cut-ofi for all other modes, so that the TM mode is truly dominant. The internal corrugations 419 of section 411 are tapered and made shallower at both ends thereof and the section diameter is concomitantly enlarged to smoothly connect into the pipes 418, 418. A purified wave in the TMoi mode is thereby obtained at the outputs of filter 411 and pipe 418'.

The operation of corrugated section 411 as a transmission mode discriminating filter is explained thereby. Since a smooth circular guide 16 418, as shown at the left of Fig. 47, transmits the TM01 wave and is necessarily large enough to also pass a TEM; wave, it is important to be able to filter out the undesired TEm component. Other methods of stopping the TElO mode by resonant filters have the disadvantage that they are relatively sharp in band width and give a limited amount of protection. When the corrugated pipe filter 411 of Fig. 47 has the right proportions for rendering the transverse magnetic mode dominant, it will not transmit the TEm wave, and any amount of attenuation to the transverse electric mode TEm may be introduced, depending only on the length of corrugated section.

IX. Antenna arrays If a small discontinuity is present in the corrugated surface, there will be radiation at that point. A number of such discontinuities constitute a radiating array. The amplitude of the radiation from any point is determined by the size of discontinuity, and the phe se by its position.

Thus, in Fig. 48 the corrugated rod 48! has regular discontinuities or enlargements 482 spaced apart a wavelength, which cause radiation and constitute a broadside array, with directivity perpendicular to its length, but non-directional in a plane perpendicular to it. If the phase velocity were made small, one protuberance 482 per wavelength would be sufficient, but if desired, the nature of the discontinuity could be reversed every half wavelength as at 483, where the corrugation is shallower, and twice the number of discontinuities obtained. The shallower discs or rings 483 constitute impedances of opposite sign to the impedance of the enlarged discs 482. The angle of the essentially conical beam of such an array from a plane could be varied by changing the phasing of the discontinuity elements. The plane of polarization ofthe radiation would normally be parallel to the rod 484, but could be altered depending upon the nature of the discontinuity.

In Figs. 49 and 49A, a number of discontinuities in the form of posts 49! are made to protrude from the rod 485 at close intervals, spire ling along it with a pitch of one wavelength. These may then be so phased that only horizontally polarized waves would be excited.

Fig. 50 shows a plane array using a corrugated sheet 500 excited from a line source, such as a reflecting sectoral parabola 50!, and a coaxial probe antenna 503. The parabola 50! is fastened to the sheet at one edge 504. Discontinuities in the corrugations 502 may be made to produce the radiation, and the pattern may be controlled by varying the position and size of the corrugated discontinuities to give a desired shape such as a pencil beam, or a cosecent squared pattern. Its advantage over other radiators is that it would be easier to make and hold a flat corrugated surface, than a curved surface such as other microwave antennas required.

By decreasing the depth of corrugations continuously along the length of the externally corrugated guide 500 (or its equivalent, the corrugated rod) an end-fire radiator similar to the polyrod can be obtained. The wave on a corrugated surface 500 with corrugations one-eighth wavelength or so deep is closely confined to the surface, but as the corrugations 502 are made i more shallow, the field extends further from the 1 surface and the wave goes faster, approaching the free-space velocity. When the depth becomes very small, the wave approximates a plane wave.

X. Microwave generators cylinder 553. The beam can finally beab'sorbed in the Wa1ls5l4 of the corrugated guide, which may be continued outside of the vacuum tube to conduct the energy to the load. Alternatively, the output wave may be propagated over a conventional wave guide or microwave radio relay link. This method of exciting the wave directly in the corrugated guide, by the beam of moving electrons is made possible by the fact that the traveling wave can be made to go as slow as desired, so that a practical beam velocity may be used. Since the electron beam travels continuously in the outward direction, only the outward wave is excited and no termination at the beginning of the corrugated guide is necessary.

Fig. 51B shows a similar application of the corrugated surface to a radially swept electron beam tube of the type disclosed in the United States Patent 2,408,437, issued October 1, 1946, to J. W. McRae and in United States Patent 2,381,539, issued August '7, 1945, to R. V. L. Hartley.

Referring to Fig. 51B, which shows a harmonic generating electron beam tube 519, the externally corrugated circular guide or ring-shaped trough 520 corresponds to the ring-shaped guide or cavity of the aforementioned McRae and Hartley patents. The corrugations 52! are regularly arranged and radially disposed like spokes of a wheel, between the circumferential rings 522, 523. Radial coupling slits 524 are provided between adjacent corrugations and at the base of the trough 520, for wave energy transfer to a rectangular corrugated guide 525 having an arcuate trough 526 with radially disposed corrugations 52'! and coupling slits 528 for matching and coupling with corresponding elements of the trough 526. The arcuate trough 526 is similar in structure to the ring 520.

The electron gun and beam rotating or defiecting electrodes in Fig. 51B are of the type disclosed in the aforementioned McRae and Hartley patents. A signal transceiver 530 is connected to a modulating grid 53 of the electron beam tube l9.

The beam of electrons is rotated with a writing or angular velocity to match the electromagnetic wave propagated around the closed annulus of the ring-like trough 520 to provide for a mutual exchange of energy between the electrons and waves. The waves are then coupled from the annular trough 520 into the corrugated guide 525 by coupling slits 524, 528 as shown, or by means of loops or dipole probes, not shown. The tube of Fig. 513 has the advantage that the electron beam may be continuously excited without requiring so large a writing velocity, and accurate focussing into a narrow slit as in the prior art tubes. The beam dimensions may be as large asnoneehalf a wavelength or so, radially. andzof the. order r of one-quarter wavelength 1 along :the circumference. of the. sweep. I he extentxof cthe field above the corrugated 'zsurface'is not: great (aboutqlt for /gA deep plateg .sowthatexcessive beam velocitieswou'ld not be necessary.

Fig. 51C..shows.-a traveling wave tube iutilizing corrugated pipe modes of wave propagation.

Traveling wavetube Mei-is of thezgeneral type disclosed in the :United :Statesp-atent application Serial No. 640,597, filedflanuary. 11, 1946-;by J. R. Pierce. The heated filament 5M, accelerating grid. 542 andiocussingcylinder 543 form the emitted electrons into an electron beam, which interacts in lenergy-eX-changewith electroma netic waves propagating from the corrugated wave guide input 544 into'the' main wave guide 546.:. The regularly spacedcorrugations 54.5'ifunction toreduce the. velocity of input wave. to.:the point where it and the electron beam velocity along the principal axis of wave guide 545!- are substantially equal. Interaction or exchange of energy between the moving electrons and the traveling wave occurs in a manner to provide an amplified electromagnetic wave derived at the output corrugated guide 546. The amplified output Wave may then be transmitted to a useful load by conventional or corrugated wave guide or by radio relay link methods. The timing pistons 54?, 548 and electron collector 549 are like those as disclosed in the aforementioned application Serial No. 640,597, filed January 11, 1946, by J. R. Pierce.

It should be understood that the corrugated guide also has properties which make it useful as a frequency discriminating filter, either highpass, low-pass, band-pass or band-stopping. As such it has advantages in that it is possible to connect smoothl into. the filter with no critical irises, etc.

It should be understood that in the various forms of corrugated surfaces heretofore disclosed, provision may be made for filling the corrugations with dielectric material wholly or partially to permit the use of shallower corrugations without thereby departing from the spirit of the invention.

It should be understood that the corrugated hollow pipes may likewise be filled with a fluid or solid dielectric without departing from the spirit of the invention.

What is claimed is:

1. A converter from internal to external wave transmission comprising a hollow wave guide adapted to propagate electromagnetic waves through its interior, a corrugated plate connected to the exterior surface of said guide and extending therebeyond for confining the external wave propagation adjacent thereto, a portion of said plate having slots between adjacent corrugations for coupling the internal and external waves, said slots extending through the wall of said wave guide. 1

2. The structure of claim 1 wherein an end of said hollow guide is closed.

3. The structure of claim 1 wherein said hollow guide is provided with regularly spaced internal corrugations on a face opposite said slots.

4. The structure of claim 1 wherein said hollow guide is provided with tapered corrugations and a series of regular corrugations of equal size, said regular corrugations being opposed to said slots.

5. A wave guide comprising a cylindrical pipe having internal and external corrugations there- 'tions.

on for propagating electromagnetic waves therealong, the depth and width of said corrugations adapted to confine the wave energy adjacent said cylinder, a source of microwaves connected to one end of said cylinder, and slots arranged between said corrugations for converting from internal to external propagation with respect to said cylindrical pipe.

6. The structure of claim 5, wherein said in- ..ternal corrugations are located on the side of said pipe opposed to said slots and external corruga- CASSIUS C. CUTLER.

Name Date Clavier July 14, 1942 1 Number Number 4 2,388,906 2,395,560 2,404,745 2,405,437 2,415,807 2,422,184 2,432,093 2,435,804 2,438,119 2,439,527 2,453,414 2,460,090 2,474,137 2,477,510 2,527,477 2,567,718 2,567,748 2,576,835

Name Date Corderman Nov. 13, 1945 Llewellyn Feb. 26, 1946 Roberts July 23, 1946 Leeds Aug. 6, 1946 Barrow Feb. 18, 1947 Cutler June 17, 1947 Fox Dec. 9, 1947 Spooner 1 Feb. 10, 1948 Fox Mar. 23, 1948 Paulson Apr. 13, 1948 De Vore Nov. 9, 1948 Kennenberg -1 Jan. 25, 1949 Young June 21, 1949 Chu July 26, 1949 Clapp Oct. 24, 1950 Larson Sept. 11, 1951 White Sept. 11, 1951 Hewitt Nov. 2'7, 1951 

